Fossil oils that provide essential fuels and raw materials for industry are finite resources. Accordingly, there is a need for the development of sustainable and renewable sources of lipid compounds to be used for the production of energy and as industrial feedstocks (Campbell et al., Scientific American 1998:78-83).
Bio-renewable oils, such as plant-derived oils, are already major agricultural commodities. Two plant-derived fatty acids, erucic acid and lauric acid, have been competing with petroleum alternatives for many years. Historically, cost has been the major bottleneck limiting the development of new plant-derived oils. Accordingly, in the context of the escalating cost of crude oil and also the increasing concerns about both finite supply and security of supply, there is an emerging strategic need to develop additional renewable products from plant, algae or microorganisms.
There are considerable environmental and economic drivers to develop new and improved bio-based chemicals. Particularly, considering the lubricant industry, vegetable oils are considered a good source of natural lubricants; however their main disadvantages are their poor low temperature fluidity behavior and sensitivity to oxidation at high temperatures. For these reasons vegetable oils are limited in what they can be used for in applications up to 120° C. (Maleque et al., Industrial Lubrication and Tribology 2003, 55:137-143). The main cause of the poor temperature properties of vegetable oils is their molecular structure, i.e., the presence of double bonds on the alkyl side chains and the central β-CH group on the glycerol molecule. The β-hydrogen atom is easily eliminated from the molecular structure through oxidation, which also leads to a weakening of the otherwise very stable ester linkage, and to further degradation of the oil (Wilson, Industrial Lubrication and Tribology 1998, 50:6-15; Wagner et al., Applied Catalysis A: General 2001, 221:429-442).
Double bonds on the carbon chain are especially reactive and react with molecular oxygen to form radicals that lead to polymerization and degradation. Polymerization increases the viscosity of the oil, which reduces its lubrication functionality. Degradation results in breakdown products that are volatile, corrosive and diminish the structure and properties of the lubricants (Kodali, Industrial Lubrication and Tribology 2002, 54:165-170). Inclusion of functional groups such as hydroxyl or branched fatty acids in the base oil itself can therefore improve the properties of the oils. For example, the irregularity imparted by hydroxyl groups or branched-chain fatty acids can disrupt the lipid packing ability of the hydrocarbon chains, thereby reducing the melting temperature of the oil.
Branched-chain fatty acids are carboxylic acids with a methyl or ethyl branch on one or more carbons that can be either chemically synthesized or isolated from certain animals and bacteria. While certain bacteria, such as Escherichia coli, do not naturally produce branched-chain fatty acids, some bacteria, such as members of the genera Bacillus and Streptomyces, can naturally produce these fatty acids. For example, Streptomyces avermitilis and Bacillus subtilis both produce branched-chain fatty acids with from 14 to 17 total carbons, with the branches in the iso and anteiso positions (Cropp et al., Can. J. Microbiology 46: 506-14, 2000; De Mendoza et al., Biosynthesis and Function of Membrane Lipids, in Bacillus subtilis and Other Gram-Positive Bacteria, Sonenshein and Losick, eds., American Society for Microbiology (1993)). However, these organisms do not produce branched-chain fatty acids in amounts that are commercially useful, production is limited to short-chain branched-chain fatty acids, and products having particular branches on particular carbons are not available or cannot be isolated in meaningful quantities.
As such, there remains a need for commercially useful branched-chain fatty acids produced from alternative sources, e.g., engineered microorganisms.